Method and Device for Cleaning Drill Cuttings

ABSTRACT

A method and a device are for cleaning drill cuttings comprising cuttings and oil-based drilling mud, wherein a significant proportion of the drilling mud is removed from the drill cuttings. The method comprises: disposing the drill cuttings in a receptacle; vibrating the receptacle until particle fluidization of the drill cuttings takes place; maintaining the drill cuttings in a particle-fluidized state during the subsequent treatment; adding a soap to the drill cuttings allowing, the soap to flow through the drill cuttings whilst the drill cuttings are particle-fluidized; draining liquid from the receptacle; and then emptying cleaned drill cuttings out of the receptacle.

This invention concerns a method for cleaning drill cuttings. Moreparticularly, it concerns a method for cleaning drill cuttings, whereinthe drill cuttings comprise cuttings and oil-based drilling mud, andwherein a significant proportion of the drilling mud is removed from thedrill cuttings. The invention also comprises a device for carrying outthe method.

During drilling operations in connection with petroleum is recovery,significant amounts of oil-based drilling mud are used. The drilling mudflows to surface entraining cuttings from the drilling operation in theborehole.

A significant proportion of the drilling mud is immediately separatedfrom the drill cuttings, whilst the drill cuttings with the remainingproportion of oil-based drilling mud is treated separately.

Relatively stringent statutory requirements prevent the drill cuttingsfrom being discharged into the surroundings. It is known to reintroducedrill cuttings in a slurrified state into a borehole, but a significantproportion of the drill cuttings are shipped to treatment facilities forsuch cuttings.

According to prior art, the drill cuttings are cleaned further viacentrifuging, washing by means of chemicals, or via thermal treatment.Current statutory requirements require that the residual proportion ofoil must be less than 10 g/kg of dry substance for allowing the cuttingsto be disposed into the surroundings.

It is obvious, particularly when offshore drilling operations areinvolved, that transport and subsequent treatment of the drill cuttingsare costly and environmentally dubious, insofar as transport and atleast some of the known cleaning operations require significant amountsof energy.

The object of the invention is to remedy or to reduce at least one ofthe disadvantages of the prior art.

The object is achieved in accordance with the invention, and by virtueof those features disclosed in the following description and in thesubsequent claims.

A method for cleaning drill cuttings comprising cuttings and oil-baseddrilling mud is provided, wherein a significant proportion of thedrilling mud is removed from the drill cuttings, the method beingcharacterized in that it comprises:

-   -   disposing the drill cuttings in a receptacle;    -   vibrating the receptacle until particle fluidization of the        drill, cuttings takes place;    -   maintaining the drill cuttings in a particle-fluidized state        during the subsequent treatment;    -   adding a soap to the drill cuttings;    -   allowing the soap to flow through the drill cuttings whilst the        drill cuttings are particle-fluidized;    -   draining liquid from the receptacle; and    -   then emptying cleaned drill cuttings out of the receptacle.

Herein, particle fluidization (or soil liquefaction) implies a state inwhich relatively dry material is brought, by means of vibration, into astate within which it flows like a liquid. Hereinafter, the termfluidized is used to mean particle-fluidized.

Upon fluidizing the drill cuttings by means of vibration, the solidbodies of the drill cuttings, herein termed particles, will be broughtinto a wearing engagement with each other, thereby liberating a part ofthe oil-based drilling mud from the particles. Addition of soap to thefluidized drill cuttings contribute to the drilling mud releasing itsbond. to the particles. The process is described in more detail in thespecific part. of the document.

Normally, the soap is mixed with water in accordance with the supplier'suser instructions. Soaps marketed under the trademarks “Safe Surfe Y”,“Safe Surfe E” and “Safe Surfe NS” from the firm M-I Swaco AS, as wellas “Cleanwall WRC” from the firm Unitor AS, may prove applicable for thepurpose.

The method may further comprise allowing the drill cuttings to compactin the receptacle before emptying. By so doing, the proportion of soapand drilling fluid is further reduced from the drill cuttings beforeemptying of the receptacle.

The method may further comprise separating the soap from the drainedliquid for re-use. Upon carrying out such a process step, theconsumption of soap may be reduced significantly.

The method may be carried out by means of a receptacle for treatment ofdrill cuttings, wherein the receptacle is connected to a frame structureand. is provided with a supply of drill cuttings, and an outlet openingfor treated drill so cuttings, and wherein the receptacle ischaracterized in that it is restrictedly movable relative to the frameand is provided with at least one vibrator and also a soap supply.

The at least one vibrator may be dimensioned in a manner allowing it tovibrate the drill cuttings into a fluidized state.

The soap supply may comprise a distribution pipe having several outletopenings for allowing it to distribute the soap within the drillcuttings. The distribution pipe may be located in the lower portion ofthe receptacle, whereby the soap is prompted to flow upwards through thedrill cuttings during the treatment. The vibration inflicted on thedrill cuttings so as to bring the drill cuttings into the fluidizedstate, contributes to the soap rising up and out of the drill cuttings.

The receptacle may be connected to the frame structure by means of anelastic element. In some cases, the receptacle may be connected directlyto a supporting structure without the presence of a separate framestructure. In such cases, and in context of the claims, the supportingstructure is to be viewed as the frame structure.

The at least one vibrator may be comprised of e.g. an eccentric motor ora pneumatic vibrator. In some cases, an ultrasonic vibrator may besuitable.

The method and the device according to the invention allow so drillcuttings to be cleaned to a purity which is better than the statutoryrequirements for disposal thereof. The device requires relatively littlespace and may, advantageously, be located at e.g. a drillinginstallation offshore.

Hereinafter, an example of a preferred method and embodiment isdescribed and is depicted in the accompanying drawings, wherein:

FIG. 1 shows a flow chart of a facility for practice of the invention,wherein also components known per se for pre-treatment of drill cuttingsare shown; and

FIG. 2 schematically shows a section through a receptacle for treatmentof drill cuttings.

In the drawings, reference numeral 1 denotes a receptacle for treatmentof drill cuttings, which is connected to a frame structure 4 by means ofelastic elements 2, see FIG. 2.

The receptacle 1 is further provided with two vibrators 6 and a soapsupply 8 connected to a distribution pipe 10 having openings 12. Thedistribution pipe 10 is disposed in a lower portion 14 of the receptacle1. The soap supply 8 is connected to a soap pump 16.

The receptacle 1, at an upper portion 18 thereof, is provided. with asupply opening 20 for drill cuttings, and an outlet 22 for soap anddrilling mud. This outlet 22 may be connected to a hose with a float(not shown) in the receptacle 1.

The receptacle 1, at the lower portion 14 thereof, is provided with aclosable outlet opening 24. Herein, the outlet opening 24 is formed witha butterfly valve 26 operated by means of an actuator 28.

FIG. 1 schematically shows a treatment facility 30 which, besides thereceptacle 1 with associated components, also shows other components forcleaning drill cuttings, the treatment facility of which constitutes,herein, a pre-treatment facility 32 within which the drill cuttings aretreated before being led into the receptacle 1, see below.

The pre-treatment facility 32 comprises a drill cutting cleaner 34,typically in the form of a rotary screen being supplied drill cuttingsvia a supply 36. The treatment may comprise several successive phases ofthe same type. A first drill cutting pipe 38 connects the drill, cuttingcleaner 34 to a centrifuge 10 from which a second drill cutting pipe 42extends to the supply 20 on the receptacle 1.

The drill cutting cleaner 34 is provided with a first pump 44 which isconnected, via a pipe 46, to a first separator 48 (or decanter). A pipe50 is connected between the centrifuge 40 and the pipe 46. Thecomponents 34, 40 and 48 constitute parts of the pre-treatment facility32.

A third drill cutting pipe 52 extends between the first separator 48 andthe second drill cutting pipe 42, whereas a first fluid pipe 54 isconnected between the first separator 48 and an intermediate tank 56 forcleaning oil. A pipe 57 for water is also connected to the separator 48.A second pump 58 is connected, via a second fluid pipe 60, to the drillcutting cleaner 34. The intermediate tank 56 may be provided with aseparation unit (not shown) in order to separate various oil types.

A third fluid pipe 62 having an outlet pump 63 extends from the outlet22 on the receptacle 1 and onto a second separator 64, whereas an outletpipe 66 is connected to the outlet opening 24 on the receptacle 1.

A fourth fluid pipe 68 extends from the second separator 64 and onto theintermediate tank 56, whereas a first soap pipe 70 extends from thesecond separator 61 and onto a soap tank 72, and an outlet 74 alsoemerges from the second separator 64.

The soap pump 16 on the soap tank 72 is connected, via a second soappipe 76, to the soap supply 8 on the receptacle 1.

The treatment facility 30 is controlled by means of a control facility(not shown). Energy supplies and control operations are known to askilled person and are not described in further detail herein.

The drill cuttings to be cleaned, and which contain oil-based drillingmud, may contain approximately 20% water and approximately 10% oil whenconveyed, via the supply 36, to the drill cutting cleaner 34. Asignificant proportion of the oil is located in pores and in a filmsurrounding the cutting particles.

In the first cleaning step, which is carried out in the drill cuttingcleaner 34, cleaning oil from the intermediate tank 56 is supplied viathe second pump 58 and the second fluid pipe 60. The cleaning oil maycomprise base oil, diesel oil or vegetable oil. By so doing, the drillcuttings are washed in cleaning oil.

The drill cuttings are then conveyed via the first drill cutting pipe 38onto the centrifuge 40 within which oil, in a second cleaning step, isseparated from the drill cuttings until the drill cuttings containapproximately 5% oil, the drill cuttings being conveyed onto thereceptacle 1 via the second drill cutting pipe 42.

Oil and water separated. from the drill cuttings flow onwards from thedrill cutting cleaner 34 via the first pump 44 and the pipe 46, and alsofrom the centrifuge 40 via the pipe 50, and onwards onto the firstseparator 48 from which oil is so returned via the first fluid pipe 54and onto the intermediate tank 56, and drill cuttings are conveyed ontothe receptacle 1 via the third drill cutting pipe 52, whereas water isdrained via the pipe 57 and possibly via a filtering facility (notshown).

When the drill cuttings are located in the receptacle 1, the thirdcleaning step is initiated by pumping-in soap from the soap tank 72 bymeans of the soap pump 16, and via the second soap pipe 76, the soapsupply 8, the distribution pipe 10 and the openings 12.

In this step, vibration from the vibrators 6 brings the relatively drydrill cuttings into a fluidized state. Some enclosed droplet-shaped oilrises up between the particles.

In a fourth cleaning step, soap is circulated through the receptacle 1.This contributes to dissolve the oil film on the particles simultaneouswith oil, which is released from pores and the surface of the particles,is being transported upwards and out of the receptacle 1. In this step,the particles rub against each other, the action of which is alsothought to promote separation of oil-containing drilling mud from thedrill cuttings. The higher density of the particles relative to that ofthe soap cause the drill cutting particles to displace the soap andsubstantially remain in the lower portion 14 of the receptacle 1. Thus,the amount of particles entrained with the soap and the drilling mud soas to discharge via the outlet 22, is relatively modest.

In the fifth and last cleaning step, the supply of soap is closed.Residual soap and other fluids rise to the surface as the drill cuttingsgradually compact in the lower portion 14 by means of vibration. Thiscompacting further contributes to “squeeze” soap and drilling mud out ofthe drill cuttings. The reason for this is that smaller particles fillspaces between larger particles during compaction and, hence, reduce theavailable volume between the particles.

Upon having drained the fluid from the receptacle 1 by means of theoutlet pump 63, the butterfly valve 26 is opened by means of theactuator 28, whereby cleaned drill cuttings may fall out of thereceptacle 1 via the outlet pipe 66.

The soap-oil-drilling mud mixture discharging from the receptacle 1flows via the third fluid pipe 62 and onto a second separator 64. Soapflows from the separator 64 onto the soap tank 72 via the first soappipe 70, whereas oil flows onto the intermediate tank 56 via the fourthfluid pipe 68, and cleaned drill cuttings fall out via the outlet 74.

The amount of cleaned drill cuttings discharging via the outlet 74 issmall relative to the discharge via the outlet 66.

1. A method for cleaning drill cuttings comprising cuttings andoil-based drilling mud, wherein a significant proportion of the drillingmud is removed from the drill cuttings, wherein the method comprises:disposing the drill cuttings in a receptacle; vibrating the receptacleuntil particle fluidization of the drill cuttings takes place;maintaining the drill cuttings in a particle-fluidized state during thesubsequent treatment; adding a soap to the drill cuttings via outletopenings in a distribution pipe located within the drill cuttings in thereceptacle; allowing the soap to flow upwards through the drillcuttings, which is due to a higher density of the drill cuttingsrelative to that of the soap, whilst the drill cuttings areparticle-fluidized; draining liquid from an upper portion of thereceptacle; and then emptying cleaned drill cuttings out of a lowerportion of the receptacle.
 2. The method according to claim 1, whereinthe method further comprises locating the distribution pipe in the lowerportion of the receptacle.
 3. The method according to claim 1, whereinthe method further comprises allowing the drill cuttings to compact inthe receptacle before emptying.
 4. The method according to claim 1,wherein the method further comprises separating the soap from thedrained liquid for re-use.
 5. A device for a receptacle for treatment ofdrill cuttings comprising cuttings and oil-based drilling mud; whereinthe receptacle is connected to a frame structure; wherein the receptacleis restrictedly movable relative to the frame structure; wherein thereceptacle is provided with at least one vibrator dimensioned in amanner allowing it to vibrate the drill cuttings into aparticle-fluidized state when disposed in the receptacle; wherein thereceptacle is provided with a supply of drill cuttings, and also anoutlet opening for treated drill cuttings disposed at a lower portion ofthe receptacle; wherein the receptacle is provided with a soap supply(8) comprising a distribution pipe having several outlet openings;wherein the distribution pipe is located within the receptacle fordistribution of soap within the drill cuttings, thereby allowing thesoap to flow upwards through the drill cuttings, which is due to ahigher density of the drill cuttings relative to that of the soap,whilst the drill cuttings are particle-fluidized; and wherein thereceptacle is provided with an outlet located at an upper portion of thereceptacle for draining liquid from the receptacle.
 6. The deviceaccording to claim 5, wherein the receptacle is provided With a supplyopening for drill cuttings, wherein the supply opening is located at theupper portion of the receptacle.
 7. The device according to claim 5,wherein the distribution pipe is located in the lower portion of thereceptacle.
 8. The device according to claim 5, wherein the receptacleis connected to the frame structure means of an elastic element.